In image processing, dynamic range generally refers to the range of tonal values in a scene that can be captured in the image. Thus, an image having a wide dynamic range will have a wide range of tonal values so that details such as highlights and shadows are easily discernable even in the brightest and darkest portions of the image.
The primary building block of a digital image formed by an image sensor is a pixel. Each individual pixel generally has a color filter above it. The filters are arranged in a pattern over a pixel array on the image sensor. One well known filter pattern is Red, Green, Green, Blue (RGGB). Another pattern, although less widely used is Red, Green, Blue and White (RGBW). The pixels of an image sensor are semiconductor devices such as photodiodes that collect incident light photons in photosites or wells. The photons are transformed into electrical charge that will serve as current signals proportional to the intensity of light or number of photons collected in the well.
The dynamic range of an image sensor is defined as the ratio between the full well capacity of a pixel in the image sensor divided by the noise floor. The full well capacity of the pixel refers to the greatest amount of photons the pixel can hold before saturation, after which information about the image is lost, while the noise floor generally refers to the readout noise of the pixel. Various factors can contribute to limiting the dynamic range of an image sensor. For example, the RGBW pattern is more ideal for low light conditions than the RGGB pattern because it has a pixel specifically for sensing white light. However, because white light includes the full spectrum of visible light, pixels that sense white light saturate much earlier than pixels that sense only red, green or blue wavelengths, thus limiting the dynamic range of the image sensor. These problems are typically made worse the greater the intensity of light.